Window regulators, which operate to open and close a moveably mounted window in a motor vehicle window opening, take a variety of forms including cable regulators which employ cables actuated by a drive means, such as a hand crank or electric motor. In cable regulators, a cable drive drum causes movement of the cable upon rotation of the drive drum by the drive means. The cable is generally attached in some form to the window and is guided by pulleys, conduits and other types of guide means to cause movement of the window upon rotation of the drive drum.
Maintaining tension on the cable in a cable operated window regulator is important to the proper operation of the regulator. A loose cable may slip from any of the guides, causing failure of the system. In addition, a loose cable will also cause increased stress on the cable and other portions of the system resulting in uneven motion of the cable when movement of the window is initiated or when the direction of movement of the window is suddenly reversed.
A known approach to maintaining tension on the cable includes the application of a tensioning force to a conduit which encloses the cable. The tensioning force is typically applied by a spring against the conduit and indirectly causes tension in the cable by increasing the travel length of the cable. Unfortunately, the indirect tensioning of the cable by the aforesaid approach can cause increased wear on the conduit. In addition, the spring actuated mechanisms which act upon the conduit often substantially increase the complexity of the regulator, thus increasing the fixed cost of the regulator in addition to increasing the manufacturing complexity.
U.S. Pat. No. 4,235,046 entitled Window Operating Mechanism to Hess et al. discloses a cable tensioning device which applies a tensioning force directly to the cable. In FIG. 2 of Hess, a tension spring 16 appears to apply a force to a pulley 5 to create tension in a cable 3. A pawl-and-ratchet device prevents return motion of the pulley when the cable is under compression. While the device of FIG. 2 in Hess maintains tension on the cable, it appears to do so only in one direction. Tension on the cable is increased, and maintained by the ratchet-and-pawl device, but is not decreased. The result may be excessive tension on the cable, which increases friction and wear and requires greater force to lift the window. Moreover, such device does not adequately self-adjust for sudden changes in loading, such as when the window operator starts to open a window and then abruptly closes the window. There is accordingly, a need for a window regulator assembly which overcomes the deficiencies noted above.
It is an object of the present invention to provide a window regulator assembly which maintains adequate tension on a drive cable in the assembly used to obtain movement of the window, while reducing the attendant complexity, cost and component wear introduced by systems as described above. This object and other objects of the invention will be apparent from the following disclosure and detailed description of certain preferred embodiments.